This invention relates to composite ceramics, and more particularly to composite ceramics which have high electroconductivity and are amenable to electric discharge machining.
Because of their outstanding ability to resist heat and oxidation, ceramics are attracting keen attention as heat resistant materials and as materials for structural members for use in machines. For the production of oxide ceramics of high strength and high density, the hot molding process otherwise known popularly as the hot press process is generally accepted as a suitable method. However, with this process only molds of relatively simple shape can be used for the molding of the raw materials so that manufacture of ceramic parts of complicated shape is difficult. Thus, the hot press process has limited applicability. As another method available for the production of ceramics, the firing process which obtains ceramics by firing raw materials in an atmosphere of air or some other gas has found widespread adoption despite its incapability of conferring as high strength upon the produced ceramics as the hot press process. This aerial firing process entails undesirable phenomena such as shrinkage due to firing and, therefore, cannot easily be used to produce parts of high dimensional accuracy in a single step of firing.
In both of the aforesaid conventional processes it is necessary first to produce a sintered body approximating the desired shape and then to machine the sintered body to high accuracy. Unfortunately, these sintered masses or ceramics are generally very brittle. Because of this particular fault, they cannot be so readily shaped by machining as metal materials and can only be machined at limited speeds with inferior dimensional accuracy. To ensure thorough exploitation of the various outstanding properties of ceramics and promote extensive utility of ceramics in applications to various structural members, therefore, development of a process capable of machining ceramics in desired shapes with as high accuracy as is obtainable with metal materials and/or development of novel materials of ceramics amenable to machining with high accuracy are prerequisites. In the manufacture of parts of heat exchangers, valves, toothed wheels, and gas turbine blades, for example, three-dimensional machining is as important as any other simple shaping operation. With metal materials, the electric discharge technique permits the curved surfaces of such parts to be shaped accurately and, therefore, enables die members of complicated shape to be effectively manufactured. Most ceramics are, however, of inferior electroconductivity and cannot be machined by the electric discharge method.
One object of this invention is to provide ceramics which are as amenable to electric discharge machining as metal materials.